The process of coplanar dielectric barrier discharge (DBD) has been investigated experimentally and theoretically by using a segmented-electrode system. The local discharge current, light emission intensity and the developing velocity of plasma on the cathode were obtained. The results of the experiment and the two-dimension fluid modeling are compared. It was shown that there exists a non-uniform field in plasma region which causes the disagreement between the local discharge and the light emission during the discharge development in coplanar DBD. The secondary electron emission producod by photon bombardment on the dielectric surface should be taken into account in studying DBD.